Alkyl esters of methanesulfonic acid are known to be involved in reaction with DNA. Pharmaceutical active substance in the form of mesilate and medicinal product containing such API needs control on the presence of alkyl mesilates.

In PRI the method for detection of trace of ethyl and isopropyl methanesulphonate has been elaborated for this purpose. Gas chromatography coupled with mass spectrometry is applied. Reference materials – ethyl and isopropyl mesilates were synthesised in PRI. The analysis is performed by spiking test samples with reference standards and using methyl caprylate as internal standard. Acceptable amount of any alkyl mesilate in the API was set as 1 ppm.

In the first version of the method analytes were extracted from aqueous solution of API to dichloromethane and extract was ten times concentrated, then it needed 2 steps of the sample operating. In the final version of the method analytes were extracted to ethyl acetate without additional concentration. In both method extract was injected to the GCMS and analysed by selected ions monitoring mode.

LOD’s in the first version were 0.24 ppm for ethyl mesilate and 0.013 ppm for isopropyl mesilate. In the final method LOD’s were 0.012 and 0.008 ppm respectively. The latter method was then more sensitive and simpler.

The method is much simpler than pharmacopoeial one which needs derivatising of ethyl and isopropyl mesilates into iodides and using of headspace GCMS.

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